Conventionally, as described in Japanese Published Patent Application No. 2000-123487, a filter coefficient update means in an optical disc playback apparatus takes a difference between a provisional data judgement output that is obtained from a provisional judge unit and an output signal that is equalized by a filter, as an equalization error signal, and updates a filter coefficient so as to minimize an average of squares of the equalization error signal to improve the quality of the equalized signal.
However, in recent years, as the amount of information is increased, demand for higher-density recording is growing in optical discs, and a land/groove recording method is employed by which information is recorded in both of grooves 901 which are arranged in a recording area 900 of an optical disc, and lands 902 between the grooves, as shown in FIG. 9. As seen from the figure, there is a difference in physical height between the groove part 901 and the land part 902. Therefore, characteristics of reproduced signals corresponding to recorded data vary due to differences in reflected lights. Accordingly, the conventional technique including only one filter coefficient learning means for controlling a filter that performs digital equalization to minimize the equalization error cannot handle the difference in characteristics of the reproduced signals between the groove part 901 and the land part 902.
When an optical disc on which data are recorded according to the land/groove recording method is played back, the conventional optical disc playback apparatus that is constructed as described above cannot accurately control the difference in characteristics of the reproduced signals, resulting from the difference in reflected lights.